The present invention relates to a method for manufacturing at least a surface layer of a multilayered trim part for attachment to a structure of a vehicle, which surface layer has a front side formed at least partially by a first surface portion, which has a first colour, and by a second surface portion, which is situated at least partially against the first surface portion and which has a second colour different from the first colour. The surface layer is in other words a two- or multicolour surface layer. The method for manufacturing such a surface layer is a moulding method wherein a first layer forming the first surface portion is produced against a first portion of a mould surface while leaving a second portion of the mould surface free for producing, in a next step, a second layer forming the second surface portion against the second portion of the mould surface and at least partially also against the back of the first layer.
The multilayered trim part is for example a dashboard, a door panel, a console or another interior trim part of an automotive vehicle. Usually it consists of the surface layer bonded by means of an intermediate foam layer to a rigid substrate layer. The surface layer may consist of an elastomeric skin layer either or not provided with a thinner coloured layer, in particular a paint layer. In the method according to the invention the skin layer is moulded against a mould surface. If it is covered by an additional coloured coating layer, this coating layer is first applied, as an in-mould coating, onto the mould surface.
The surface layer can be made for example by means of a spray or a pouring process wherein a curable skin material, in particular a polyurethane reactive mixture, is sprayed or poured in a liquid state onto the mould surface. Such a method is disclosed in EP-B-0 804 327. In this known method a first layer forming material, more particularly a polyurethane reactive mixture having a first colour, is sprayed first onto a first portion of the mould surface while shielding off a second portion of the mould surface by means of a mask. In a next step, the mask is removed and a second layer forming material, again a polyurethane reactive mixture but having a second colour different from the first colour, is sprayed onto the second portion of the mould surface and partially onto the back of the previously sprayed polyurethane layer. The first layer forming material thus has an edge which is situated underneath the layer of the second layer forming material and which defines the colour transition between the first and the second surface portion of the surface layer.
A drawback of this known method is that the transition between the two colours is not always sufficiently sharp, due to sputtering or scattering of the polyurethane reactive mixture underneath the mask. EP-B-0 804 327 therefore discloses to provide the transition between the two colours onto an upstanding ridge of the mould surface in order to hide the transition zone between the two colours from view. The actual colour transition is then indeed located in a groove in the surface layer of the trim part. However, due to the width of the groove, it still remains somewhat visible so that a need remains to achieve a sharp transition between the different colours.
DE-A-100 62 825 provides an improvement of the method disclosed in EP-B-0 804 327. In the method disclosed in this German patent application, the surface layer is produced by spraying a first paint layer onto a first portion of the mould surface, by spraying a second paint layer onto a second portion of the mould surface and partially onto the back of the first paint layer, by pouring a polyurethane reactive mixture onto the back of both paint layers and by closing the mould to allow the polyurethane reactive mixture to cure in a closed mould. When spraying the first paint layer, the second portion of the mould surface is covered by means of a mask. Notwithstanding the fact that a mask is used to cover the second portion of the mould surface and hence to define the edge of the first paint layer, DE-A-100 62 825 discloses it is difficult to achieve a clear and sharp dividing line between the two colours. DE-A-100 62 825 therefore also describes to produce the transition between the two colours on top of an upstanding ridge. The improvement proposed by DE-A-100 62 825 consists in reducing the width of the thus obtained groove on the visible side of the surface layer. This is achieved by transferring the surface layer to a second mould wherein the upstanding ridge is replaced by a thin upstanding sheet. In this second mould a foam layer is moulded onto the back of the surface layer. A drawback of this method is that it does not allow a direct back-foaming process and that a second, expensive mould is therefore always required to perform the backfoaming process.
Another method making use of the mask technology to produce a multicoloured trim part, is disclosed in US-A-2004/0099988. In this method, a first paint layer is sprayed onto a first portion of the mould surface and a second paint layer on a second portion of the mould surface, which was covered with a magnetically securing mask when spraying the first paint layer. A third material, usually a polyurethane material, is then applied, usually sprayed, over the first and second paint layers to form a backing layer. In this known method the transition between the two colours is also produced on top of an upstanding ridge to hide the colour transition from view.
A drawback of the prior art methods set forth hereabove is that, due to the use of a mask, defects arise at the transition or parting line between the different colours, i.e. either some of the first layer forming material will arrive onto the second mould surface portion when removing the mask, this is the so-called bridging problem, or, when such bridging is avoided by maintaining a distance between the mould surface and the edge of the mask, some of the first layer forming material will arrive underneath the edge of the mask causing a scattered transition zone between the different colours. The use of upstanding ridges on the mould surface, to hide these colour transition zones from view, involves an important limitation of the design possibilities. Moreover, the use of upstanding ridges do not enable flat colour transitions. A further drawback of the prior art methods is that the used mask technology is critical and complex. In order to get the colour transition line as good as possible, the mask geometry has to be tailored accurately to the three-dimensional shape of the mould surface and in particular to the geometry of the upstanding ridges. Any deviation in both geometries will be translated in inaccurate colour transitions.
A method wherein a surface layer for a trim part is produced without the use of a mask is disclosed in U.S. Pat. No. 5,328,349. In this known method a multicoloured slush skin is produced by a powder-slush process. According to this US patent, masking techniques can be used for producing multicoloured slush skins but it has been shown in actuality that the separating seam looks untidy to the eye. In the disclosed method, the entire mould surface is therefore first covered with a first thermoplastic material, a portion of produced slush skin is cut out and removed from the mould surface and a second thermoplastic material is moulded onto the free mould surface and onto the back of the first thermoplastic material. An important drawback of such a method is that it is only applicable for thermoplastic materials. Moreover, it is a quite complex process and, in the disclosed method, the actual colour transition has still to be produced on top of an upstanding edge.
Other methods which are only applicable for thermoplastic materials are disclosed in JP 59142112 and in U.S. Pat. No. 5,073,325. In these known methods a pattern recessed in the mould surface is first filled up with a thermoplastic material. In a next step, the entire mould surface is covered with a second thermoplastic material so that the front side of this second thermoplastic material has a decorative feature formed by the first thermoplastic material. A drawback of these methods is also that the first thermoplastic material has to be applied always in a pattern recessed in the mould surface and, moreover, after having applied the first material in the recessed pattern, any excess of material outside the recessed pattern has to be removed. A further drawback of these known methods are the limited design possibilities due to the fact that the second thermoplastic material extends always on both sides of the decorative feature. It is thus for example not possible to produce a surface layer consisting of two main surface area's of different colours.